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RCA All-Band Antenna




 
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Steve - K4HX
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« on: December 18, 2012, 11:08:01 AM »

In the November 1952 edition of the RCA Ham Tips there is an article, "An All-Band Antenna and Coupler" detailing an open-wire fed folded dipole system for 80/75, 40, 20 and 10 meters. A drawing from the article is attached below. I thought I would model this antenna to see what it does. The height of the top wire in the system was placed at 45 feet above ground. The results follow.

80m (3.8 MHz)

Z: 13.021 - i 55.526  TO: 90 deg  (omni)

40m (7.2 MHz)

Z: 719.940 + i 5809.200   TO: 18 deg at  90 deg az

20M (14.2 MHz)

Z: 1331.600 + i 323.650   TO: 24 deg @ 0 deg az

15M (21.2 MHz)

Z: 421.960 + i 1041.900   TO: 43 deg @ 0 deg az

10M (28.5 MHz)

Z: 486.720 + i 292.750    TO: 12 deg @ 36 deg az

The pattern break up is not bad on the higher bands. There are just two main azimuthal lobes on 40 and on 20 meters. Even on 15 meters there are only two, albeit at a higher than normally desired take-off angle. Finally, on 10 there are four major lobes. A regular 80 meter dipole would give you four major lobes and four minor lobes. The major lobes are far more narrow with a dipole than with the RCA antenna.

The patterns for each of the bands are attached. Note that on 40 meters the major lobes are turned 90 degrees from the rest of the bands (i.e. the pattern is in line with the wires instead of broadside or at right angles). The system is working like a pair of verticals here.

Another nice thing about the RCA antenna is that it's only 52 feet in length, so it's a nice options for those cramped for space.

Anyway, just something to think about for those who might be considering an 80-10 meter open-wire fed dipole system.


* rcaallbandant.png (86.76 KB, 700x373 - viewed 970 times.)
* RCA Allband Patterns.pdf (785.05 KB - downloaded 437 times.)
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Steve - K4HX
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« Reply #1 on: December 18, 2012, 11:14:16 AM »

What if the break in the top set of wires was closed creating a loop?

80m (3.8 MHz)

Z: 2365.000 + i 14007.000  TO: 90 deg  (omni)

Wow! What a nasty impedance. About the same pattern but with a little more than 1 dB less gain, assuming you could match the thing.

40m (7.2 MHz)

Z: 225.180 - i 206.82   TO: 48 deg at  0 deg az

Pattern pretty similar to a dipole at about the same height. This arrangement would be better for stateside and local work and the folded better for DX.

20M (14.2 MHz)

Z: 114.890 - i 576.410   TO: 23 deg

Very similar pattern to the folded design, but with about 2 dB less gain.

15M (21.2 MHz)

Z: 439.570 - i 1048.900   TO: 18 deg @ 0 deg az

Six lobes, two major ones broadside and 4 more smaller (4 db down) of the sides. A couple dB more gain than the folded design and at a better takeoff angle.

10M (28.5 MHz)

Z: 747.160 - i 997.600    TO: 12 deg @ 36 deg az

4 big lobes, about 2 dB less gain than the folded design. But the lobes are larger and less pronounced nulls with the loop.


So, it seems for 40 and 15 meters the loop connection would be better for most instances (unless you wanted to work DX on 40 meters in directions 90 degrees to the line of the wires). Yes, the loop connection does have more lobes on 15 but the two main lobes are at a better takeoff angle. The difference between the two is a wash on 20 and 10 meters, although the folded connection does have slightly more gain. The impedance on 40 and 20 meters is better with the loop connection and slightly better on 10 meters. The impedances are about a wash on 15 meters.

Being able to switch between the two configurations would make this system very versatile.
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